1. Field of the Invention
The present invention relates to a fuel cell which performs an electrochemical reaction between gaseous fuel and oxygen in the atmosphere by using a polymer electrolyte layer.
2. Related Background Art
A fuel cell has been put into practical use which is obtained by stacking fuel cell units in which an electrochemical reaction between hydrogen gas and oxygen in the atmosphere is performed by using a polymer electrolyte membrane formed of a carbon fluoride polymer carrying a sulfonic group.
Japanese Patent Application Laid-Open Nos. 2000-285934 and 2004-171967 each disclose a technique of forming such a fuel cell formed by stacking a number of fuel cell units.
Japanese Patent Application Laid-Open No. 2004-536438 discloses a technique of distributing and supplying hydrogen gas as a fuel.
In the fuel cell disclosed in Japanese Patent Application Laid-Open No. 2000-285934, a sealing structure surrounding a through-hole exclusively for supplying hydrogen gas and a through-hole extending across an oxidizer supply space reduces a ratio of an area of a power generation region to an area of a fuel cell unit. A region exclusively for fastening disposed outside a hydrogen gas supply space and a region exclusively for supplying hydrogen gas disposed inside the hydrogen gas supply space reduce the area of the power generation region in which the hydrogen gas supply space and the oxidizer supply space oppose each other through a polymer electrolyte membrane.
Therefore, only a small power generation region can be obtained in comparison with the area of the whole of the fuel cell unit, so that the output per unit volume, unit weight, and unit production cost of a fuel cell obtained by stacking the fuel cell units is small.
The fuel cell disclosed in Japanese Patent Application Laid-Open No. 2004-171967 requires provision of a sealing structure for a hydrogen gas supply path in a position distant from a sealing structure provided outside a fuel supply space. Therefore, the number of seals and spacers for isolating the hydrogen gas supply space from the atmosphere increases, and the sealed length also increases, thereby reducing the reliability of the sealing. Further, because the alignment of the planes of the fuel cell units is performed by use of a single fastening member (through bolt) at the center while securing a supply path of a fuel to be supplied to the fuel supply space, a thick fastening member having a complex structure, that is, an expensive fastening member is required. The thick fastening member increases the area of the through-hole to reduce the ratio of the area of the power generation region to the area of the fuel cell unit.
In the fuel cell disclosed in Japanese Patent Application Laid-Open No. 2004-536438, because a fastening structure of a fuel cell unit is disposed outside the fuel cell unit, the number of components increases compared with those of Japanese Patent Application Laid-Open Nos. 2000-285934 and 2004-171967. The ratio of the area of the power generation region to the area of the fuel cell unit including the fastening structure is further reduced.
In view of such circumstances, there is a need for a fuel cell which can increase the ratio of the area of a power generation region to the area of a fuel cell unit to increase output per unit volume and unit weight of the fuel cell. Further, there is also a need for a fuel cell which can increase output per unit production cost and can be produced with a small number of components without requiring highly precise assembly.